1. Field of the Invention
The present invention relates to an ultrasound diagnosis apparatus for use in the field of medical treatment, and more particularly to setting of a plurality of sub arrays on an array transducer.
2. Description of Related Art
Ultrasound diagnosis apparatuses are used in the field of medical treatment for the purpose of diagnosing diseases of a living body (a patient). More specifically, ultrasonic diagnosis apparatuses transmit an ultrasonic pulse to a living body and receive a reflected wave therefrom for forming an ultrasonic image based on a receiving signal obtained by the reflected wave received.
A two-dimensional (2D) array transducer (or transducer array) is used for effecting two-dimensional scanning of ultrasonic beams to thereby form a three-dimensional echo data acquisition space within a living body. A 2D transducer is generally composed of a plurality of transducer elements arranged along X and Y directions.
In some 2D array transducers, a plurality of sub arrays are defined on the 2D array transducer for the purpose of channel reduction of a transmission/reception section, simultaneous formation of a plurality of reception beams, or like purposes. Conventionally, a plurality of sub arrays are fixedly defined on the 2D array transducer. For example, a plurality of sub arrays having a rectangular shape are set with respect to a 2D array transducer, and in this case, the shape of each sub array cannot be changed. Japanese Patent Laid-Open Publication No. 2001-276064 discloses grouping of a plurality of transducer elements in which the structure of each group is fixed. Japanese Patent Laid-Open Publication No. 2001-104303 discloses a structure for performing phase adjusting and summing (or beam formation) in two stages. Japanese Patent Laid-Open Publication No. Hei 9-322896 discloses, in FIG. 6, that a plurality of groups are fixedly set for a 2D array transducer, that a plurality of first beam formers are connected to the plurality of groups, and that a plurality of second beam formers are provided at a stage subsequent to the plurality of first beam formers. U.S. Pat. No. 5,832,923 discloses that a plurality of 2D sub arrays are defined on a 2D array transducer and that a plurality of groups are defined on each sub array. None of these documents, however, describes dynamically changing the shape of each sub array and the grouping patterns.
When the shape of the sub array or the grouping pattern is defined uniformly or fixedly, there arises a problem of the inability to obtain a beam profile preferable for specific transmission and reception wave conditions. For example, side lobes may tend to be generated in a specific beam scanning direction. European Patent Laid-Open Publications EP-1491913-A2 (corresponding to Japanese Patent Laid-Open Publication No. 2005-34634) and EP-1491914-A2 (corresponding to Japanese Patent Laid-Open Publication No. 2005-34633) disclose that a plurality of sub arrays are set on the array transducer and that a plurality of groups are set for each sub array. In this technique, each group is basically composed of a plurality of transducer elements, and a common transmission signal is supplied to the plurality of transducer elements. A plurality of reception signals supplied from the plurality of transducer elements forming each group are summed together, and a resultant reception signal obtained by summing is subjected to a delay process. European Patent Laid-Open Publication EP-1491913-A2 listed above further describes changing of the shape of each sub array in accordance with the beam scanning direction. None of these documents, however, describes dynamically changing the grouping pattern in accordance with the depth of a focus point.
In order to achieve an excellent focus, desirably, the structure of each group (i.e. the grouping pattern within each sub array) is set such that, for a plurality of transducer elements forming each group, which are connected in parallel with each other (i.e., have the same delay time), acoustic distances between a focal point and the respective transducer elements are made as equal as possible. The acoustic distance from the focal point to each transducer element changes with the beam address and the depth of the focal point (e.g., a transmission focal point). It is therefore desired to dynamically change the shape of the sub array and the grouping pattern in accordance with such a change in the beam scanning conditions.